Fix ssl npe

[CrazyHZM]

What is the purpose of the change

Brief changelog

Verifying this change

Checklist

• Make sure there is a GitHub_issue field for the change (usually before you start working on it). Trivial changes like typos do not require a GitHub issue. Your pull request should address just this issue, without pulling in other changes - one PR resolves one issue.
• Each commit in the pull request should have a meaningful subject line and body.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Check if is necessary to patch to Dubbo 3 if you are work on Dubbo 2.7
• Write necessary unit-test to verify your logic correction, more mock a little better when cross module dependency exist. If the new feature or significant change is committed, please remember to add sample in dubbo samples project.
• Add some description to dubbo-website project if you are requesting to add a feature.
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• If this contribution is large, please follow the Software Donation Guide.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.04%. Comparing base (d192c7b) to head (4aa7c45).
⚠️ Report is 10 commits behind head on 3.0.

Files with missing lines	Patch %	Lines
...bbo/remoting/api/PortUnificationServerHandler.java	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                3.0   #11092      +/-   ##
============================================
+ Coverage     66.01%   66.04%   +0.03%     
- Complexity      317      319       +2     
============================================
  Files          1240     1240              
  Lines         54041    54042       +1     
  Branches       8179     8180       +1     
============================================
+ Hits          35673    35691      +18     
+ Misses        14508    14494      -14     
+ Partials       3860     3857       -3     

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[EarthChen]

LGTM